Replace views::MouseEvent with ui::MouseEvent

ash/system/tray/system_tray.cc

Index: ash/system/tray/system_tray.cc
===================================================================
--- ash/system/tray/system_tray.cc	(revision 151406)
+++ ash/system/tray/system_tray.cc	(working copy)
@@ -477,12 +477,12 @@
   return true;
 }
 
-void SystemTray::OnMouseEntered(const views::MouseEvent& event) {
+void SystemTray::OnMouseEntered(const ui::MouseEvent& event) {
   TrayBackgroundView::OnMouseEntered(event);
   should_show_launcher_ = true;
 }
 
-void SystemTray::OnMouseExited(const views::MouseEvent& event) {
+void SystemTray::OnMouseExited(const ui::MouseEvent& event) {
   TrayBackgroundView::OnMouseExited(event);
   // When the popup closes we'll update |should_show_launcher_|.
   if (!bubble_.get())